Post-natal stem cells (meaning those present after birth) are unspecialized cells that can renew themselves extensively and develop into more mature cells having specialized functions. Stem cells may be induced under certain physiologic or experimental conditions to become cells with special functions, such as the beating cells of the heart muscle, or the insulin-producing cells of the pancreas. The process by which a stem cell becomes a cell with special functions is known as differentiation. Differentiation can be induced through use of multiple signals that can include chemicals secreted by other cells, physical contact with neighboring cells, and certain molecules in the microenvironment. Thus, stem cells can be treated with specific signals to become specific types of cells having useful functions. These newly differentiated cells can then be used to generate replacements for cells that are lost through normal wear and tear, injury, or disease. For example, stem cells show promise for treating diseases such as Parkinson's disease, diabetes, and heart disease. Stem cells have multiple applications in medicine and dentistry. Accordingly, new sources of stem cells, and methods for their use are needed.